The sequence and acknowledgment number fields are both 32-bit fields that hold TCP sequence numbers. Unlike UDP, where the source port number is optional, both the source and destination ports must be present in the TCP header. The source and destination port numbers hold the TCP port numbers of the sending and receiving process for the TCP segment. Urgent pointer: If the URG flag is set, this 16-bit field points to a place in the byte stream that contains data that the application has defined to be urgent. Ĭhecksum: The 16-bit checksum is the Internet checksum of the data, the TCP header, and the IP destination and source addresses.
Window: The 16-bit window field holds the amount of bytes that the receiver is able to receive.